Vulcanization of rubber



Patented June 6, 1933 UNITED STATES PATENT OFFICE HENRY H. HARKINS, OFRIVER EDGE, NEW JERSEY, ASSIGNOR TO THE NAUGATUCK CHEMICAL COMPANY, OFNAU'GATUCK,

NECTICUT CONNECTICUT, A CORPORATION OF CO1\T' VULCANIZATION OF RUBBER NoDrawing. Application filed June 19,

This invention relates to the vulcanization of rubber and similarvulcanizable materials and to the resulting products, and moreparticularly to the provision of an improved 5 process for thevulcanization of the same in the presence of an accelerator andcompounds or compositions with which to effect the purpose of theinvention.

A new class of activators has now been found for organic accelerators,and more particularly for those of the ultra or semiultra type asrepresented by thiazyl sulphides, among which are themercapto-arylthiazoles, benzothiazyl monosulphides, benzothiazyldisulphides and polynitro aryl benzothiazyl sulphides such as 2-4dinitrophenyl benzothiazyl sulphides. The activators when used inconjunction with the desired accelerator in the vulcanizing operationpermit of a reduction in the usual amount of the accelerator withoutlosing the benefits of vulcanization that are attainable Where theaccelerator is used without the activator. Further advantages of theinvention will be apparent from the hereinafter set forth description.

The activators broadly are salts of ammonia and strong acids, and moreparticularly such salts having the property of re- 30 tarding thevulcanization of a mixture of rubber and sulphur. Thevulcanizationretarding salts of ammonia have now been found to comprisethe salts of ammonia and acids, which acids have a primary dissociationconstant equal to or greater than that of oxalic acid.

For the purpose of illustrating the invention, the following examples inwhich the 40 parts are by weight are given Without limiting it theretoExample ].The following table shows the activating influence of ammoniumchloride with reduced amounts of an organic accelerator(mercaptobenzothiazole) 1931. Serial No. 545,495.

with ammonium chloride A B C D E Smoked sheet 100 100 100 100 100 Carbonblack 50 50 50 50 Zinc oxide 13 13 13 13 13 Pine tar 5 5 5 5 5 Stearicacid 1.25 1.25 1. 25 1. 25 1. 25 Sulphur 3. 5 3. 5 3. 5 3. 5 3. 5Mercaptobenzothiazole 1. 25 1.0 .75 .5 .25

CURE m 301$ STEAM PRESSURE Green tensile 2922 2962 1638 Too poor Toopoor to test to test 3722 3817 3355 2745 Too poor to test 4066 3937 37523245 2090 4036 4173 3987 3202 2683 3920 3882 3853 3302 2023 3910 40403930 3462 3210 Same formu1a+ A m m 0 n i u m chloride 5 75 1. 0 15 30323361 2998 Too poor Example 2.The following table shows the activatinginfluence of ammonium chloride in a stock such as represented undercolumn B, Table I, having the steartic acid replaced by ammoniumchloride.

Table II.Effect of varying ammonium chloride using one part ofmercaptobcneofliiaeoie and leaniag out stem-i0 acid Stearie acid 1. 25Mercaptobenzothiazole 1. 00 1 00 1.00 1.00 1.00 Ammomum chloride. 5 1.00 1. 25

CURE AT 303 STEAM Green tensile E sample 5.The invention is furtherillustrated by the following tables which show the use of low and highamounts of zinc oxide, and that stearic acid may be replaced withammonium chloride:

Table III.A.cfi'vatioa with ammonimn chloride in (1 purc (mm stockMercaptobenzothiazol 8 .8 .8

CURE AT 30 srmn Green tensile Smoked sheet 100 100 100 100 100 Zincoxide... 13 13 13 I 13 13 Sulphur 3. 5 3. 5 J. 5 3. 5 3. 5Mercaptobenzothiazole 1 1.0 .75 .50 .25 Stearic acid 1 25 1. 25 1. 25 1.25 1, 25 Ammonium chloii e. .75 .75 .75 .75 cons AT :1 s'rmn PRESSUREGreen tensile Same formula without ammonium chloride Green tensile 9 Ewample ,4..The following table shows the relative abrasion resistingvalues obtainable with a stock of the type shown in l able 1, usingstearic acld, accelerator and anmionium chloride as shown:

Table v Stearic acid 1.25 1. 25 2. 25 1.25 1.25 Mercaptobenzothiazolm.1.25 1. 25 1. 25 1.25 1.25 1.25 Ammonium chloride" .5 5 1v 25 10 .30Rating "160% 105% 103% 107% 103% 105% Example 5.-Table VI shows howresistance to abraslon of a low zinc stock may be improved by the use ofammonium chloride, and also how the accelerator may be reduced to .5part when 1t is properly activated, w th no loss in resistance toabrasion.

Table VI Smoked sheet 100 100 100 100 Carbon black... 50 50 50 .10 Pinetar 5 5 5 5 1 1 1 l Zinc oxide 2 2 2 2 Zinc soaps of fatty acids 2 2 2 2Mercaptobenzothiazole. 1. 25 1. 25 .75 50 Antioxidant 1 1 p l p 1Sulphur 3. 5 3. 5 3. 5 3. 5 Ammonium chloride". .7 .5 ,5 ,5 Resistanceto abrasion 100% 110% 105 7 102% served latex, on mercaptobenzothiazole:

0f part of in ammonia- Tablc 1"II.-I'hc delimiting influence ammoniumchloride when present Iuzca: sprayed rubber (whale) Whale withoutammonium chloride Whale with 1 part oichloride Zinc oxide Sulphurlklercaptobenzoi i Green tensile This data show that ammonium chloride,when sprayed with ammonia latex, exerts some activating effect onmercaptobenzothi azole.

lation, spray drying, or otherwise.

The invention presents manifold advantages.

Tensiles have been obtained by using 0.5 part of mercaptobcnzothiazoleand .75 part of ammonium chloride per 100 parts of rubber (smoked sheet)which are as high as where 1 part or mercaptobcnzothiazolo is usedalone. This allows a reduction of about one-half in the acceleratorcost. Also rubber stocks containing as low as 2 parts 01' zinc oxidehave been found to cure well when containing such as ammonium chlorideand an accelerator such as mercaptobenzothiazole, with improvement inabrasion resistance of irom 8 to 10%. The invention further allows theomission in tire tread compounds of such as stearic acid withsubstantially no lowering of tensiles or green abrasive values. Thenon-use of such as stearic acid removes a source of blooming in thevulcanized stocks.

The invention has been found to be particularly useful in thevulcanization of rubbers which contain a sub-normal percentage of latexserum solids when compared with normal. latex, for example such assmoked sheet,

pale crepe and creamed rubbers.

acetate, ammonium trichloracetate,

monium oxalate, within the broad scope of the invention. The resultsobtained with the am monium halide are particularly effective, an d morenotably that with ammonium chloride.

The invention may be employed in connec tion with latex (natural orartificially prepared) aswell as solid rubbers for the production offinished rubber goods. Materials of this invention may be mixed in anydesired manner at any stage prior to the actual vulcanizing operation.It is also clear that various softeners, anti-agers and othercompounding ingredients may be used in corn junction with theaccelerator and activator.

The invention disclosed may be used in the preparation of inner tubes,tires, thread, hose, dipped goods, chemical goods, latex or articlesmade from latex, etc.

With the detailed description given above, it will be obvious thatmodifications will suggest themselves without departing from theprinciple of the invention, and it is not desired to limit the inventionotherwise than as set forth in the appended claims.

Having thus described my invention, what I claim and desire to protectby Letters Patent is:

1. A process of producing vulcanized rubher which comprises vulcanizingrubber containing sulphur, zinc ozide and mercaptobenzothiazole in thepresence of ammonium halide.

2. A process of producing vulcanized rubher which comprises vulcanizingrubber containing sulphur, zinc oxide and mercaptobenzothiazole in thepresence of ammonium chloride.

3. A vulcanized rubber product resulting from the process set forth inclaim 1.

4. A vulcanized rubber product resulting from the process set forth inclaim 2.

5. A vulcanization accelerator mixture comprising a thiazyl sulphidevulcanization accelerator and the ammonium salt of an acid having adissociation constant not less than that of oxalic acid.

6. A vulcanization accelerator mixture comprising a thiazyl sulphidevulcanization accelerator and the ammonium salt of a mineral acid havinga dissociation constant not less than that of oxalic acid.

7. A vulcanization accelerator mixture comprising a benzothiazylsulphide accelerator and the ammonium salt of a mineral acid having adissociation constant not less than that of oxalic acid.

8. A vulcanization accelerator mixture comprising amercaptobenzothiazole vulcanization accelerator and an ammonium halide.

9. A vulcanization accelerator mixture comprising mercaptobenzothiazoleand ammonium halide.

10. A vulcanization accelerator mixture comprising mercaptobenzothiazoleand ammonium chloride.

11. A process of producing vulcanized rubber which comprises adding torubber prior to vulcanization a vulcanizing agent, an or- 6 ganicaccelerator, and the ammonium salt of an acid normally capable ofretarding the vulcanization of a mixture of rubber and sulphur, andvulcanizing the rubber.

12. A process of producing vulcanized rubber which comprises adding torubber prior to vulcanization a vulcanizing agent, an organicaccelerator, and the ammonium salt of an acid having a dissociationconstant not less than that of oxalic acid, and vulcanizing the rubber.

13. A process of producing vulcanized rubber which comprises adding torubber prior to vulcanization a vulcanizing agent, an ultra orsemi-ultra organic accelerator, and the ammonium salt of an acid havinga dissociation constant not less than that of oxalic acid, andvulcanizing the rubber.

14. A process of producing vulcanized rubber which comprises adding torubber prior to vulcanization a vulcanizing agent, an ultra orsemi-ult'a organic accelerator, and the ammonium salt of a mineral acidhaving a dissociation constant not less than that of oxalic acid, andvulcanizing the rubber.

15. A process of producing vulcanized rubber which comprises adding torubber prior to vulcanization a vulcanizing agent, a thiazyl sulphidevulcanization accelerator, and the ammonium salt of a mineral acidhaving a dissociation constant not less than that of oxalic acid, andvulcanizing the rubber.

16. A process of producing vulcanized rubber which comprises adding torubber prior to vulcanization a vulcanizing agent, amercaptobenzothiazole vulcanization accelerator, and the ammonium saltof a mineral acid having a dissociation constant not less than that ofoxalic acid, and vulcanizing the rubber.

Signed at Passaic, county of Passaic, State of New Jersey, this 16th dayof June, 1931.

HENRY H. HARKINS.

